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A panel of distinguished scientists, appearing at a Capitol Hill briefing organized by AAAS, surveyed a broad range of data and research that affirm a clear human link to global climate disruptions.

While climate change science has been subject to sometimes vitriolic attacks in recent months, the briefing took a tempered tone. The speakers emphasized the value of bucking conventional scientific wisdom, but showed that the arguments commonly used by climate change skeptics tend to fall apart when subjected to close scrutiny.

“Skepticism is an integral part of the progress of science and it helps keep the science on the correct path,” said veteran climate researcher Warren Washington, former chairman of the U.S. National Science Board. “However, skepticism without specifics, alternate hypotheses, and facts is worthless. It does not advance the science.”

But Washington and other speakers acknowledged that the reputation of climate scientists has been tarnished by the perception that they are hostile to those who reject the scientific consensus. The panelists urged their colleagues to listen carefully to skeptics and to encourage skeptics to publish their research when it meets normal scientific standards.

Warren Washington

The 11 May briefing served as a short course on what is known, and not known, about the changing climate. And it served as a reminder that, although imperfect, the scientific process, including peer review, remains the best available tool for understanding the complex workings of the natural world.

The briefing attracted about 100 staffers from congressional offices and foreign embassies, along with representatives of the U.S. State Department, the Congressional Budget Office, research universities, and non-governmental organizations. It was sponsored by 13 mainstream American science organizations representing fields ranging from chemistry and meteorology to statistics and agriculture.

The briefing was part of a continuing effort by the world science community to answer questions raised in sustained attacks in recent months. The critics’ campaign has been fueled by a handful of documented or claimed errors discovered in the massive 4th Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) and by emails apparently hacked from the Climate Research Unit at the University of East Anglia in the U.K. Though independent investigations have cleared the East Anglia researchers of any misconduct, climate skeptics have continued to use the emails as a cudgel against the entire science of climate change.

Alan I. Leshner

The briefing came just a day before U.S. Senators Joseph Lieberman (I-Connecticut) and John Kerry (D-Massachusetts) introduced a broad energy and climate bill.

“We all have come to believe that the issue of climate change and what we do about it—particularly as it relates to the issue of energy—is among the most pressing and important issues facing not only American society, but global society as well,” he said.

Richard Alley

In addition to Washington, former head of the Climate Change Research Section at the National Center for Atmospheric Research, the panel included two extensively published climate researchers: Richard Alley, the Evan Pugh Professor of Geosciences at Pennsylvania State University; and Richard Smith, the Mark L. Reed III Distinguished Professor in the departments of statistics and biostatistics at the University of North Carolina at Chapel Hill.

Washington, in the opening presentation, listed arguments commonly offered by skeptics. For example: Temperature records are inaccurate. There is no global warming. Or, at any rate, humans are not causing it. The emails from the University of East Anglia prove climate change is a fraud. There is no scientific consensus.

Richard Smith

Smith and Alley deconstructed those arguments and concluded they are in error.

Many measures show a warming world

Warming, Alley said, is a matter of basic physics: Increase the concentration of carbon dioxide, methane, and other greenhouse gasses in the atmosphere, and the atmosphere will hold in more heat.

Thousands of scientists at research centers in many countries have taken thermometer readings on land, at sea, in the atmosphere, and by satellite, he said. Others have documented “mass loss” in glaciers worldwide, rising seas, and a shift of plants and animals into warming areas at higher elevations or closer to the poles.

The inescapable conclusion: The world is getting warmer. And while changes thus far have been slight, Alley said, they will be much more substantial unless humans dramatically reduce greenhouse gas emissions. [See slide 17 from Alley’s presentation.]

The climate scholars also assessed more specific claims made by skeptics:

The “hockey stick” is wrong. Research shows that temperatures globally were largely flat for 900 years before spiking during the 20th century. Charts that track the change show a line shaped like horizontal hockey stick. But climate skeptics have persistently attacked this finding, and some have claimed that there were statistical errors in the derivation of the hockey stick shape. But Smith argued that these criticisms of the hockey stick themselves used simplistic statistical analysis, and that if these analyses are taken further, the hockey stick again appears.

In addition, multiple studies by other researchers, using different techniques and approaches, have found the same spike, and an assessment by the U.S. National Research Council vindicated the science that produced the “hockey stick” findings.

There’s been no warming since 1998. Both Alley and Smith detailed how skeptics had drawn this conclusion based on an eight-year period following 1998. But, they said, that research is misleading because no reliable conclusions can be drawn from temperatures in such a short period.

Rather, Alley said, trends are usually inferred from time-blocs of at least 30 years, so that inevitable year-to-year variations don’t have a disproportionate effect on the overall picture.

Smith looked at the temperature data through several different statistical lenses and found “no evidence” of a decrease in temperatures after 1998. “If anything,” he said, “the [warming] trend increases after this time.” Alley concurred.

The CO2 is coming from volcanoes. Analysis of the atmospheric gasses shows that steadily rising CO2 concentrations come not from volcanoes, Alley said, but from the burning of organic matter, especially fossil fuels. Volcanic emissions amount to only 1-2% of human emissions, he said.

The emails from the University of East Anglia show a conspiracy by climate scientists. Alley said that skeptics have been selective and unreliable in their use of the materials hacked from the university’s Climate Research Unit. About 1000 private emails covering a span from 1996-2009 were reviewed by the skeptics, and they have focused most attention on about 10. And those, Alley said, have been “grossly taken out of context.”

[Two independent studies, including one by the U.K. House of Commons Science and Technology Committee, have concluded that there was no scientific wrongdoing by the university researchers.]

“A lot of what of what they [skeptics] say—at first sight it might appear that they’re making reasonable points,” Smith said. “If you look more closely… a lot of what they say doesn’t stand up to scrutiny.”

Added Alley: “The whole climate community has spent 30 years trying to find a way out of this. Could the sun be doing it? Could the volcanoes be doing it? Could cosmic rays be doing it? But…we can’t explain what has happened recently without us—it has our fingerprints.”

Reassuring the public and policymakers

Still, researchers at the briefing were concerned with a more overarching misimpression advanced by skeptics: that the science of climate change could be undone by one or two narrow attacks.

“The results do not depend on one fact, one data set, one investigator,” Alley countered. “Instead, the major results depend on multiple lines of evidence from many investigators in many counties, in many labs, using many techniques, woven together and assessed by many groups.

“The many, many threads of evidence woven into these results mean that no single error could change them—break the ‘hockey stick,’ or discredit the Climate Research Unit (at the University of East Anglia), or erase one or a few climate scientists from history, and the main results would be unaffected.”

But even after dismissing the skeptics’ arguments, the scientists at the briefing acknowledged that the attacks have tarnished the credibility of climate researchers and their work. And data alone will not resolve that challenge, they agreed.

They suggested that science could take a number of steps to assure the public and policymakers that the science is transparent and non-partisan.

“We have to continue to improve our methods and the accuracy of scientific information that’s given to policymakers,” Washington said. “We must continue to rely on independent reviewers. [We need to] work extra hard to obtain the input of skeptics…. All climate data should be made freely available for testing by others.”

While the conclusions of the four IPCC reports “are not in doubt,” Washington said, “clearly there needs to be a process that can correct errors that are later found in a massive document.” And, he added, a review underway by the InterAcademy Council is expected to lead to tighter procedures when the IPCC begins its next round of assessment this fall.

“Let’s hear the skeptics’ viewpoints.”

Though the speakers defended the record of the climate science community, each agreed that the community should be committed to hearing—and publishing—conclusions that challenge mainstream views.

“Robust criticism is an inevitable and necessary part of the scientific process,” Smith said. “It would be amazing if all the world’s scientists agreed on every detail of the research. Nevertheless, some suspicions have been raised that perhaps some of the contradictory viewpoints haven’t been given enough of an airing. My viewpoint is, let’s hear the skeptics’ viewpoints. I don’t think there’s any reason to exclude them from either the scientific literature or public discourse.”

Washington described the dilemma faced by one journal editor when a peer-review panel was split on a paper that raised questions about an aspect of climate change science. Washington said he urged the editor to publish the paper, even though its arguments made him uncomfortable.

“I think we should err on the side of making sure that the skeptics do have a voice,” he said.

“Peer review is not always perfect,” Leshner added, “but it is the best of what we’ve been able to come up with…. There is a tendency of peer review to be somewhat conservative, and I would echo Warren Washington’s point that research ought to be judged on the quality of the science and not on the palatability of the answer.”

But the speakers at the briefing agreed that high scientific standards are crucial to credibility with policymakers and the public. And if skeptics want their work to have impact, they must meet those standards—conducting research, writing papers, and submitting their research for evaluation in the peer-review process.

“I do believe that climate skeptics should publish their results in scientific journals,” Smith said, “and not in blogs and other unofficial outlets.”

The briefing, “Climate Change: Key Questions and Answers,” was sponsored by AAAS; the American Chemical Society; the American Geophysical Union; the American Statistical Association; the University Corporation for Atmospheric Research; the American Institute of Biological Sciences; the American Meteorological Society; the American Society of Agronomy; the Crop Science Society of America; the Ecological Society of America; the Geological Society of America; the National Ecological Observatory Network; and the Soil Science Society of America.